The field of the invention is esters and processes of making same and the present invention is concerned with a method for preparing asymmetric aliphatic ketones. A mixture of two aliphatic carboxylic acids is reacted at higher temperatures in the presence of an oxidic metal catalyst to produce a ketone mixture in which the preparation of the desired asymmetric ketone is predominant as follows: ##STR1##
The state of the art of the synthesis given in equation (I) may be ascertained by reference to British Patent 1,194,057; French Patent 1,533,651; U.S. Pat. No. 3,468,956; TETRAHEDRAN LETT. 1972, pp. 257-260; and the Kirk-Othmer "Encyclopedia of Chemical Technology" 2nd Edition, Vol 12 (1967) p. 125.
As disclosed in British Patent 1,194,057, the initial input is an aldehyde in addition to the acid and the reaction takes place in the presence of water. Again in French Patent 1,533,651 costly aldehydes are used as initial inputs.
Another production method is described in TETRAHEDRAN LETT. 1972, pp 257-260. Therein suitable secondary alcohols are dehydrogenated into the corresponding ketones. The availability of the required secondary alcohol is problematical here.
Again, using a mixture of carboxylic acids to produce ketones has been described. U.S. Pat. No. 3,468,956 uses polyphosphoric acid in the temperature range between 100.degree. and 300.degree. C. as the catalyst. Many authors employ radioactive thorium oxide catalysts.
Kirk-Othmer i.b.i.d. discloses that unsymmetrical dialkyl ketones are prepared by passing vapors of two different fatty acids over an alkaline earth oxide at elevated temperatures. It is stated that the product necessarily contains the three possible ketones and in the example given a mixture of acetic acid and butyric acid are reacted in the vapor phase at 300.degree. C. on a manganese dioxide catalyst to produce 16% methyl ethyl ketone, 24% propyl butyl ketone and 60% ethyl propyl ketone.
Accordingly the known methods require either initial substances which are costly at least in part, or catalytic systems which are commercially unsuitable.